The present invention relates generally to electronic musical instrument keyboard apparatus including a mechanism for causing a mass body unit to pivot in response to depression operation of a corresponding key.
Heretofore, there have been known electronic musical instrument keyboard apparatus of a type in which a mass body unit is caused to pivot in response to depression of a key to provided a key touch feeling, i.e. feeling of mass and feeling of stop, similar to those provide by a keyboard mechanism of an acoustic piano (see, for example, Japanese Patent Application Laid-open Publication No. HEI-9-198037, which will hereinafter be referred to as “patent literature 1”).
FIG. 6 is a schematic right side view of a conventionally-known electronic musical instrument keyboard apparatus, which includes white keys 1, black keys 2 and a key frame 61. The key frame 61 has stepped portions formed at front and rear ends regions thereof as viewed in a longitudinal direction of the keys, and a horizontal portion 61a located between the front and rear stepped portions. Key support section 61b is provided on a rear region of the horizontal portion, and a mass body unit support portion 61c is provided on a front region of the underside of the horizontal portion 61a. Key pivot portions 1b and 2b of the white and black keys 1 and 2 are provided on the key support section 61b for pivotably supporting the white and black keys 1 and 2. Front and rear mounting portions 61d and 61e are provide in front of and at the back of the front and rear stepped portions, respectively and mounted to a bottom plate 4 of the key frame. The bottom plate 4 is, for example, a lower case (shelf plate) of the electronic musical instrument. Vertical wall portion 61f is formed in front of the mounting portion 61d, and a key guide 5 corresponding to the white key 1 is provided on the vertical wall portion 61f. The key guide 5 is inserted in the underside of the white key 1 near the distal end la of the key 1 and functions to prevent leftward/rightward positional displacement and rolling of the white key 1. Further, a key guide 6 corresponding to the black key 2 is provided on and projecting upward from the horizontal portion 61a. A plurality of key switches 4 are provided on the horizontal portion 61a of the key frame, and a plurality of protrusions (actuators) are provided on the undersides of upper portions of the white and black keys 1 and 2 in opposed relation to the key switches 4.
Force transmitting portion 1c projects downwardly from the underside of the white key 1 and passes through a hole 61g of the horizontal portion 61a. The force transmitting portion 1c has a bottom plate provided at its distal end. Resilient member 7 is fixed to the lower surface of the bottom plate.
Mass body units 62 are provided in corresponding relation to the white keys 1 and black keys 2. The mass body units 62 are arranged under the keys 1 and 2 in parallel to one another under in a direction where the keys are arranged in parallel to one another (i.e., i.e., in a key-arranged direction). The mass body unit 62 shown in the figure corresponds to the white key 1. Each of the mass body units 62 is pivotably supported by the support portion 61c, and it is caused to pivot via the corresponding force transmitting portion 1c. 
Each of the mass body units 62 includes: a pivot point portion 62c supported by the mass body unit support portion 61c; main and auxiliary driven portions 62a and 62b of a bifurcated shape formed in front of the pivot point portion 62c and engageable with the force transmitting portion 1c of the corresponding key; an elongated connecting section 62d located rearwardly of the pivot point portion 62c; and a mass concentrating section 62d provided at the rear end of the elongated connecting section 62e. Namely, the elongated connecting section 62d is joined to an upper front end portion of the mass concentrating section 62e. The mass concentrating section 62d and mass concentrating section 62e, especially the mass concentrating section 62e, produce a great moment of inertia as the mass body unit 62 pivots.
The mass concentrating section 62e has a horizontal lower surface portion that can uniformly collide against a later-described lower-limit stopper 9. The mass concentrating section 62e also has an upper surface portion slanting downward toward its rear end, and this upper surface portion can uniformly collide against a later-described upper-limit stopper 10. The above-mentioned main and auxiliary driven portions 62a and 62b are held in engagement with the force transmitting portion 1c with the resilient member 7 interposed therebetween.
As the mass body unit 62 pivots in response to key depression operation by a human player, a reactive force corresponding to a moment of inertia of the mass body unit 62 is transmitted via the white key 1, so that a feeling of mass is imparted to a player's finger having depressed the key. Then, once the human player releases the finger from the depressed white key 1, the mass body unit 62 slowly pivots back to the original position (i.e., position illustrated in the figure).
Although not specifically shown, the force transmitting portion of the black key 2 overlaps the force transmitting portion 1c of the white key 1 as viewed in a direction perpendicular to the sheet of the figure. Mass body unit similar to that for the white key 1 is provided for the black key 2, and pivotably supported by the mass body unit support portion so that it can pivot via the force transmitting portion of the black key 2. Although not shown in the figure, a return spring is provided between each of the white and black keys 1 and 2 and the key frame 61.
The upper-limit stopper 10 is disposed on the lower surface of the horizontal portion 61a of the key frame. As the mass body unit 62e pivots, the upper surface of the mass concentrating section 62e collides with the stopper 10 to be stopped at an upper limit position defined by the stopper 10. Because the mass concentrating section 62e is rapidly braked, a human player's finger is imparted with a feeling of stop by way of the key.
The lower-limit stopper 9 is disposed on the upper surface of the bottom plate 4 of the key frame. As the mass body unit 62 pivots back to the initial position, the lower surface of the mass concentrating section 62 collides with the stopper 9 to be stopped at the initial position defined by the stopper 9. At this time too, a feeling of stop can be imparted to the human player's finger as long as it is kept in contact with the key.
Further lower-limit stopper 11 is disposed on a front upper surface of the horizontal portion 61a of the key frame. Once the white key 11 is fully depressed after the key switch 11 turns ON, the white key 1 is stopped at a lower limit position by left and right side surfaces of the white key 1 colliding with the further lower limit stopper 11. Such lower-limit stopper 9, upper-limit stopper 10 and further lower-limit stopper 11 each extend in a belt shape in the key-arranged direction for shared use among all of the white and black keys.
From the viewpoints of an impact absorbing capability, tone deadening capability and improved reproducibility of the stopped positions of the keys (white and black keys 1 and 2) and mass body units 62, the above-mentioned stoppers 9, 10 and 11 need to have a resilient restoring force; it has been conventional to form these stoppers 9, 10 and 11 of, for example, felt, polyurethane elastomer or the like. However, it has been known that resilient deformations are accumulated in the stoppers 9, 10 and 11 as they are compressed due to an impact applied from the mass body unit 62 and such resilient deformations would cause a reactive force (called “rebound”) to the key and mass body unit 62 such that the key would undesirably vibrate. Thus, there can not be obtained a comfortable feeling of stop. Particularly, a great reactive force would be given by the upper-limit stopper 10 that is subjected to an impact from the mass body unit 62 having pivoted by being subjected to a great key depression pressure.
Also known in the art are electronic musical instrument keyboard apparatus in which each mass body unit has a closed interior space and a multiplicity of fine weight particles are movably accommodated in the closed interior space (see. for example, Japanese Patent Application Laid-open Publication No. HEI-8-16153, which will hereinafter be referred to as “patent literature 2”). In contrast to the aforementioned electronic musical instrument keyboard apparatus, the closed interior space swings vertically downward in response to depression of the corresponding key. Thus, at the beginning of strong key depression (i.e., key depression with a great force), the fine weight particles freely fall, which produces a small inertial mass. During the pivotal movement of the mass body unit, the mass of the fine weight particles is added to the mass body unit, so that a human player can obtain a feeling of performance. Once the mass body unit collides against the lower-limit stopper, the reactive force to the human player's finger becomes very small not only because the fine weight particles function to attenuate the collision energy of the mass body unit but also because the weight of the key has decreased due to the collision. As the mass body unit pivots back into collision against the upper-limit stopper, the reactive force becomes small on the same principle as noted above so that the mass body can stop without bounding.
However, with such known electronic musical instrument keyboard apparatus, it has been difficult to greatly vary the feeling of mass during key depression operation. Besides, no effective techniques have been proposed to date for preventing mechanical sound noise from being produced by the movement of the fine weight particles and for knowing the accommodated quantity of the fine weight particles in the closed inner space of the mass body unit.